1. Field of the Invention
The present invention relates to a tandem-type laser scanning apparatus, and more specifically to a tandem-type laser scanning apparatus that is used in an image formation apparatus such as a color laser printer or color digital copier to record an image on a plurality of scanned surfaces by scanning them with a plurality of laser beams in such a way that the scanned surfaces are individually exposed to the laser beams.
2. Description of the Prior Art
U.S. Pat. No. 6,304,360 proposes a tandem-type laser scanning apparatus that forms a color image fast by scanning a plurality of photoconductors with a plurality of laser beams directed thereto by being deflected with a single deflector in such a way that the photoconductors are individually exposed to the laser beams.
The laser scanning apparatus mentioned above is so constructed that a plurality of laser beams are incident on the deflector at different angles in the sub scanning direction. This is to ease the separation of the optical paths of the individual laser beams. As a result, when the individual laser beams are incident on the deflector, they suffer different degrees of bow and wavefront twist. It is difficult to correct bow and wavefront twist simultaneously. Different degrees of bow in the individual laser beams result in color dislocation in the produced color image. On the other hand, uncorrected wavefront twist results in an unduly large beam spot, making the produced image unsharp.